The present invention relates to metal container bodies and more particularly to metal container bodies of the seamless variety comprised of a sidewall and a bottom formed integrally therewith. The container bottom has an improved design to provide for controlled flexing and distention of the same outwardly under the influence of internal pressures generated by the contents of the container or can after it has been closed and sealed.
In the past, a standard solution to the problem of providing a seamless metal can body, such as an aerosol, beer or carbonated beverage can body, with a bottom structure having the requisite strength or internal pressure-resistant qualities, has called for making substantially the entire bottom of such a can body in the form of a dome-type panel that was recessed inwardly. Containers provided with this general type of bottom structure are illustrated in such prior art patents as U.S. Pat. Nos. 2,777,125; 3,029,507; 3,360,158; 3,416,702; 3,232,260; 3,730,383; 3,731,838; 3,693,828; 3,556,032; 3,603,275; 3,701,455; 3,782,315 and 3,785,311. Alternately, seamless can bottoms have been provided with conventional reinforcing beads or rings, such as are provided in the seamless metal cans discussed at pages 26-31 of the Mar., 1952, issue of the magazine entitled "Modern Metals" and at pages 20-23 of the Feb., 1959 issue of the magazine entitled "Florida Trend," and U.S. Pat. No. 3,312,098.
When a seamless metal can body having such a bottom structure was fabricated in the past as, for example, that of U.S. Pat. No. 3,693,828, only the outer periphery of the can bottom was adapted to contact the surface upon which the can rested whereby the can had a substantial amount of stability in either a filled or empty condition.
Despite the strength and stability provided by the inwardly recessed and domed bottom in a seamless can body structure, such a bottom ordinarily required a substantial metal thickness in the starting metal blank so as to provide the requisite reservoir of metal for properly forming the bottom and the adjacent sidewall section in order to avoid deleteriously thinning of the bottom or adjacent section of the sidewall in one or more areas to the point that localized weakened areas resulted and the strength otherwise provided by the domed bottom configuration was nullified.
Another disadvantage incident to the use of prior art seamless can bodies provided with domed bottoms concerns the fact that the deeper or larger the dome, the greater the volumetric loss in the interior of the can. This volumetric loss had to be compensated for either by increasing the length of the can sidewall and/or can diameter with the consequent use of additional starting metal.
More recently, in an effort to utilize less metal material and effect a savings in container cost, while at the same time still utilizing a spherically or hemispherically domed bottom design for the purposes of reinforcing the bottom of a seamless metal can body, efforts have been made to provide a relatively deep or large reinforcing dimple or bubble in the central portion of the seamless can bottom and a relatively flattened area in the outer reaches of such bottom. When a can body provided with such a bottom was filled and sealed with a liquid under pressure, such as beer or a carbonated beverage, the can bottom was permitted to flex or bulge out in a selective fashion in a ring-like area adjacent the bubble. In other words, the can bottom rather than resisting pressure was allowed to flex outwardly in the direction of the pressure applied thereto. Such a can, for example, is shown and discussed at page 96 of "Business Week" magazine for Nov. 23, 1974, and in U.S. Pat. No. 3,904,069, issued Sept. 9, 1975.
Even in this latter type of can bottom structure, however, because of the relatively large size of the bubble used in the can bottom as commercially manufactured and discussed in the aforementioned Business Week magazine article, and when compared to the overall bottom surface area of the can and because of the decrease in capacity incident thereto, a substantial amount of metal is still required in the final can body structure even though less starting material may be used than that in the past. In other words, it can still be necessary to provide an adequate reservoir of metal for lengthening or increasing the diameter of the can sidewall as noted previously in order to compensate for loss of capacity plus the fabrication of a bubble or dome of the proper metal thickness and strength. Thus, this last noted can bottom structure as well as other and similar can bottom structures as shown in U.S. Pat. Nos. 3,369,694; 3,272,383; 3,359,841 and 3,572,271 can still be objectionable as regards the amount of material required for the bottom and sidewall structures to obtain the requisite strength, volume, etc.
The instant invention is concerned with providing a seamless metal can that is particularly advantageous as regards its being used to dispense liquids maintained under pressure. It has an improved bottom structure that can be made with a minimal metal thickness consistent with other strength and volume requirements. The instant container is also believed to have a relatively stable bottom when filled with pressurized fluid, and even when flexed or distended in the controlled manner to be described. The improved configuration of the container bottom of the instant invention is such that where the container is a drawn and ironed container it can be readily formed in the tool pack of a standard draw and iron can bodymaker and at the end of the ironing operation so that no separate and costly doming operation need be used.